â?¢ Time Warner's stock plunged 12.9% after 21st Century Fox announced it is dropping its bid for the media company. Shares of 21st Century Fox rose 2.1%.

â?¢ Sprint named Marcelo Claure as its new CEO, replacing Dan Hesse, amid reports it was calling off its merger with T-Mobile. Sprint tumbled 19% and T-Mobile US shares dropped 8.4%.

Global markets sold off sharply on fears that Russia may be amassing troops near the Ukrainian border that could lead to a dramatic escalation in hostilities there. In Europe, Germany's DAX lost 0.7%; Britain's FTSE 100 index gave up the same percentage.

In Asia, Japan's Nikkei 225 fell 1.1% to 15,159.79 and the Hang Seng in Hong Kong lost 0.3% to 24,584.13.

"We're not going to guess what's on Russia's mind, but we can see what Russia is doing on the ground - and that is of great concern," NATO spokeswoman Oana Lungescu said in an e-mail to USA TODAY on Wednesday.

NATO said that Russia has amassed around 20,000 combat-ready troops on Ukraine's Eastern border.

"The latest Russian military build-up further escalates the situation and undermines efforts aimed at finding a diplomatic solution to the crisis. This is a dangerous situation," Lungescu said.

Separately, Polish Prime Minister Donald Tusk said Wednesday that he has information - he did not elaborate - suggesting there is a growing threat of what he called "direct intervention" by Russia in Ukraine.

Stocks fell sharply on Tuesday as global tensions continued to outweigh growing evidence the U.S. economy is picking up steam.